1. Field of the Invention
The present invention relates to a method of copolymerizing cyclic olefins and vinyl olefins, a copolymer produced by the method, and an optical anisotropic film comprising the same. More particularly, the present invention relates to a method of copolymerizing cyclic olefins and vinyl olefins in a high yield, a high heat resistant copolymer produced by the method, and an optical anisotropic film comprising the copolymer.
2. Description of the Related Art
Inorganic materials such as silicon oxides or nitrides have been mainly utilized in the information and electronic industries. Recent technical developments and demands for compact and high efficiency devices need new high performance materials. In this respect, a great deal of attention has been paid to polymers which have desirable physicochemical properties such as low dielectric constant and moisture absorption rate, high adhesion to metals, strength, thermal stability and transparency, and a high glass transition temperature (Tg>250° C.).
Examples of resins for optical components, which are generally used, include a methacrylic resin, polycarbonate, polyimide, and the like. However, these resins are not suitable for high performance optical components due to disadvantages such as low thermal stability, high birefringence, and coloration.
Recently, polyacrylate, polyethersulfone (PES), polynorbornene (PNB), and cycloolefin copolymer (COC), which have a Tg of 100° C. or greater, a transmittance of 90% or more, low birefringence, and a low moisture absorption property, appeared as alternative polymers. These polymers consist of primarily a carbonyl group as a polar group and an aromatic or cyclic olefin portion as a non-polar group, and may further include fluorine (F) in order to improve physical properties such as a heat resistance, a refractive index, and a moisture absorption property.
PES is an amorphous and heat resistant engineering plastic which includes diaryl sulfone as a backbone and has a high Tg of approximately 225° C. and a strong resistance to thermal aging. PNB is made of norbornene derivatives and has a high Tg of approximately 300° C., a transparency of 92% or greater, and a low birefringence. COC (or COP) consists of a cyclic olefin and an ethylene backbone and has a Tg of 100-200° C., a high transparency, and a low birefringence, and can be subjected to extrusion and injection molding. And these have higher transparency, heat resistance, and chemical resistance and much lower birefringence and moisture absorption rate than conventional olefin polymers. Thus, this polymer can be applied to various applications, e.g., optical components such as mobile phone camera lens, CD/DVD pick-up lens, LCD light guide panel and POFs (plastic optical fibers), electronic and information components such as capacitor films and low-dielectrics, and medical components such as low-absorbent syringes, blister packagings, etc.
Meanwhile, polyacrylate has very high hardness and adhesion and high transparency, and thus is widely used in an optical field such as glass substitutes.
Thus, when norbornene is copolymerized with acrylate, a new polymer having features to be applicable to broader field can be obtained. However, a polar vinyl olefin monomer is generally polymerized through a radical or anionic initiator, whereas a norbornene monomer is addition-polymerized by a late transition metal catalyst such as Ni or Pd. Due to such a contrary polymerization characteristic of the two monomers, their direct copolymerization is difficult to carry out.
In the early days, norbornene and polar vinyl olefin were copolymerized by radical polymerization, in which the content of norbornene in the copolymer is very low (≦5.5% by weight) (Morris et al., U.S. Pat. No. 3,536,681; Starmer et al., U.S. Pat. No. 3,679,490). Thereafter, copolymerization of norborene and acrylate using a palladium catalyst was reported, but a polymerization yield is low or it is difficult to obtain reproducible polymerization results (Goodall et al., U.S. Pat. No. 6,303,724; Sen et al., U.S. Pat. No. 6,111,041 and U.S. Pat. No. 6,593,440).
Therefore, there has been a demand for a new method of producing a copolymer of norbornene and vinyl olefin with a high molecular weight and a high yield.